PCBA processing common problems

Short circuit

Refers to two independent adjacent solder joints between the solder after the formation of the phenomenon of bonding, the reason for the solder joints too close ﹑ improper design of the components ﹑ direction of the solder is not correct ﹑ solder speed too fast, insufficient flux coating and Parts of the poor solder ﹑ ﹑ poor solder paste coating, solder paste too much and so on.

2 empty welding

The sag is not stained on tin, the parts and the substrate is not welded together, the reason for this situation are welding cutting dirty ﹑ ﹑ ﹑ ﹑ feet tall, poor solder, parts bit extraneous, improper dispensing, resulting in excess glue in cutting First class, will result in air welding. PAD welding parts are mostly bright and smooth shape.

Fake welding

Parts feet and welds stained with tin, but in fact not completely caught by the tin. Mostly because the solder joint contains rosin or caused.

Cold welding

Also known as undissolved tin, due to insufficient temperature or flow soldering time is too short due to such a shortcomings can be improved by the second flow, cold solder paste surface layer of dark, mostly in powder form.

5 parts off

After the soldering operation, the parts are not in the proper place. The reasons for the soldering are as follows: selection of adhesive materials or improper dispensing operations, incomplete curing of adhesive materials, excessive tin wave and slow soldering speed.

6 missing parts

Parts should be installed without loading.

Broken

Parts of the shape of obvious defects, material defects, or caused by process damage, or parts of the process of soldering cracks. Insufficient pre-heating of parts and substrates, and excessive cooling of the solder, all contribute to the tendency of the parts to rupture.

8. Denudation

This phenomenon occurs in the passive parts, due to the end of the part of the part, the coating is not good, so when passing through the tin wave, the coating into the tin bath, resulting in the end of the structure was damaged, the solder attachment is not Good, and the higher temperature and longer soldering time, will make the erosion of bad parts more serious. In addition, the general welding temperature is lower than the wave soldering, but for a long time, so if the parts are poor, often causing denudation, the solution in addition to parts change ﹑ flow temperature and time of the appropriate control, the choice is still available Silver solder paste containing components to suppress the dissolution of the end of the part, the operation of the wave soldering solder components more convenient to change.

9 tin tip

Solder joint surface does not appear smooth continuous surface, and has sharp protrusions, which may occur because of excessive solder speed, flux coating, etc..

Less tin

Welded parts or parts feet, the amount of tin is too small.

11 ball (beads)

Tin content of the ball, PCB, parts, or parts feet. Paste quality is poor or stored too long, printed circuit board assembly improper preheating ﹑ improper paste coating and solder paste coating ﹑ preheat ﹑ flow soldering step of the operation time is too long, are likely to cause tin ball (beads).

12. Open circuit

The line through but not conduction.

13. Tombstone effect

This phenomenon is also an open circuit, easy to happen in the CHIP parts, the reason is due to the solder process, due to different parts of the welding point between the different pull, leaving the parts one end of the tilt, as both ends of the pull So different, and the amount of solder paste, soldering tin and soluble in the difference between the time.

14. Wick effect

This occurred in the PLCC parts, so the reason is that the temperature of the parts of the foot when the solder joint rise higher, faster, or welding cutting poor wettability, which makes the solder paste melting, the parts along the foot rise , Making the amount of solder joints is not enough. In addition, inadequate or not warm-up preheating, and solder paste easier to flow, will promote this phenomenon.

15. CHIP parts white

In the SMT process, the marked surface of the part value is flip-chip welded to the PCB, the value of the part can not be seen and the value of the part is correct, and the function is not affected.

16. Reverse polarity / reverse

Components are not placed in the correct direction.

17. Shift

Excessive or insufficient dispensing:

19. Stand sideways